Ok, well, you asked for it. More here.
http://fallout.wikia.com/wiki/Forced_Evolutionary_Virus
FEV is a core element of the Fallout universe and the main reason for mutations, but it is also a humanly engineered and in some cases mutated creation, the consequences made more severe due to the consequences of a great war.
BUT- I would caution that the Fallout universe is very different than that of Morrow Project. Fallout is a retro-future game- a game that is based on the type of science fiction one might have watched in the 1950s and 1960s. Sci/Fi apocalyptic type stories that might include the Forbidden Planet or Them or Panic in the Year Zero, where as a more modern view would be World War Z or Deep Impact. Or if you like the difference between the original Planet of the Apes franchise and the more current one.
That said, I think there are elements that can be mined for the Morrow Universe. Government or Corporate modified biological and genetic engineering gone mutant, with consequences and further changes since the end of the war- that would be worth exploring for a game.
One idea I have been playing with is that the trigger event of the war is a virus that essentially sterilizes women - Children of Men or White Plague- game, in which the survivors are the descendents of those who were immune or escaped but are themselves not immune. Some of the members of the MP may carry the virus unknowingly into the future, and the team has to figure out what to do about them.